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Investigation On The Thermal Effect And (Ultra) Short Pulse Laser Performance Of Concentration Gradient Composite Nd:YVO4/Nd:YVO4/Nd:YVO4 Crystal

Posted on:2017-04-14Degree:DoctorType:Dissertation
Country:ChinaCandidate:S X LiFull Text:PDF
GTID:1108330488451892Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
Laser-diode (LD) pumped all-solid-state lasers have been widely utilized in the fields of telecommunication, industrial cutting, military, and surgery due to its advantages of all solid state, high pump efficiency, high stability.The thermal lensing and thermal stress-induced birefringence make the laser cavity unstable and cause significant optical loss in the system. To reduce the thermal loss induced by the heat deposition in the gain media, we employed the multi-segment composite Nd:YVO4/Nd:YVO4/Nd:YVO4 crystal as gain dedia, the thermal effect and pulsed laser performance were investigated. Using finite element method and MATLAB, we stimulated the temperature variations in the gain media and pumping faces; employed electro-optic (EO)n acoustic-optic (AO)n GaAs and Cr4+:YAG as Q-switcher, we investigated the Q-switched laser performance of composite Nd:YVO4/Nd:YVO4/Nd:YVO4 crystal; by simultaneously employed EO/GaAs (Bi-GaAs), the fundamental frequency (second harmonic) dual-loss modulated sub-nanosecond Q-switched and mode-locking laser was investigated, and then the laser performance was simulated theoretically; then employed semiconductor saturable absorber mirror (SESAM), we demonstrated characteristic comparasion of composite and conventional Nd:YVO4 passive mode-locking lasers, and then theoretically analysed the relation between mode-locking pulse duration and intracavity energy density; by employing a non-critically phase-matched KTiOPO4 crystal, we successfully investigated an efficient eye-safe optical parametric oscillator (OPO) at 1570 nm driven by a diode-pumped acousto-optical Q-switched composite Nd:YVO4/Nd:YVO4/Nd:YVO4 laser. The main contents included in this dissertation are as follows:I By employing finite element method and MATLAB software, we firstly stimulated the temperature variations in the multi-segment composite and convertional Nd:YVO4 crystals as well as at pumping faces.II Employed the compact plane-concave cavity, the LD pumped composite Nd:YVO4/Nd:YVO4/Nd:YVO4 actively Q-switched laser at 1064 nm was realized with EO modulator. Actively Q-switched laser performances of two composite and one conventional Nd:YVO4 crystals were investigated, as average output power, pulse duration, single pulse energy and peak power versus incident pump power and the repetition rate of EO.Ⅲ LD pumped composite Nd:YVO4/Nd:YVO4/Nd:YVO4 actively Q-switched laser at 1064 nm was realized with AO modulator. To compare the laser performance of composite and one conventional Nd:YVO4 crystals, two composite Nd:YVO4/Nd:YVO4/Nd:YVO4 and one conventional Nd:YVO4 crystals were employed as gain media, the average output power, pulse duration, single pulse energy and peak power versus incident pump power were achieved.And then the active Q-switching laser performances of were compared with AO and EO modulator, the insert loss of EO was higher than that of AO, corresponding to shorter pulse duration.Ⅳ LD-pumped composite Nd:YVO4 passively Q-switched laser with GaAs wafer as the saturable absorber was successfully demonstrated, and the average output power, pulse duration, single pulse energy, and peak power were obtained with the identical transmission of OC, different initial transmissions of GaAs saturable absorber, and the augment of incident pump power.Ⅴ The passively Q-switched laser characteristic of Cr4+:YAG saturable absorber was theoretically analysis, then LD pumped passively Q-switched composite Nd:YVO4/Nd:YVO4/Nd:YVO4 lasers were presented with Cr4+:YAG as saturable absorber, under the identical initial transmission of Cr4+:YAG and disparate reflectivity of OCs, the average output power, pulse duration and repetition rate were achieved with the increase of incident pump power, and then the single pulse energy and peak power with the augment of incident pump power were calculated.Ⅳ By simultaneously employing electro-optic modulator and GaAs, the dual-loss-modulated Q-switched and mode-locking low repetition rate subnanosecond laser of the multi-segment composite Nd:YVO4/Nd:YVO4/Nd:YVO4 crystal was investigated. Beyond the threshold pump power, only one mode-locking pulse underneath a Q-switching envelope was generated, the peak power with MW magnitude was obtained. At the 1kHz repetition rate of EO, the average output power, pulse duration and pulse energy of Q-switching envelope and single mode-olocking pulse, and peak power were obtained with the variation of pump power; Considering the influence of intracavity population density, SPA and TPA of GaAs, and absorption coefficient of the different Nd3+doping concentration, the new rate equations were brought in, the number of pulse underneath a Q-switching envelope was simulated with different incident pump power, the numerical solutions were consistent with the experimental results.VII By simultaneously employing electro-optic (EO) modulator and Bi-doped GaAs, LD pumped dual-loss-modulated Q-switched and mode-locking composite Nd:YVO4/Nd:YVO4/Nd:YVO4/KTP sub-nanosecond green laser was demonstrated. With EO and different saturable absorbers, average output power, pulse duration and single pulse energy of Q-switched and mode-locking laser and single mode-locking laser were achieved with the augment of incident pump power. Compared with EO and GaAs, the doubly EO and Bi-GaAs modulated single mode-locking green laser can achieve shorter pulse duration and higher peak power.VIIIEmployed a five-mirror W-shape resonator, LD pumped composite Nd:YVO4/Nd:YVO4/Nd:YVO4 and conventional Nd:YVO4 passively mode-locked lasers at 1064 nm were generated. Employing the ABCD matrix method, the laser cavity was optimized to obtain high output power and stable mode-locking laser. During the experiment, the stable passive mode-locking lasers were obtained by the three Nd:YVO4 crystals, and then the relationship between pulse duration and intracavity power density was obtained theoretically, the theoretical analysis was in agreement with the experimental result.IX By employing a non-critically phase-matched KTiOPO4 crystal, we successfully investigated an efficient eye-safe optical parametric oscillator (OPO) driven by a diode-pumped AO Q-switched composite Nd:YVO4/Nd:YVO4/Nd:YVO4 laser. Under the fixed repetition rate, the average output power, pulse duration, single pulse energy and peak power of signal wave were achieved under the different incident pump power.The innovations of this dissertation are as follows:Ⅰ By employing finite element method and MATLAB software, we stimulated the temperature description in the multi-segment composite Nd:YVO4/Nd:YVO4/Nd:YVO4 crystals and the pumping faces for the first time.Ⅱ By simultaneously employing EO and GaAs, the dual-loss-modulated Q-switched and mode-locking low repetition rate subnanosecond laser of the multi-segment composite Nd:YVO4 crystal was investigated. Considering the absorption coefficient influenced by different Nd3+ doping concentration of the composite Nd:YVO4 crystal, the novel coupled rate equations were brought in to simulate the EO/GaAs doubly Q-switched and mode-locking sub-nanosecond laser performance of the multi-segment composite Nd:YVO4/Nd:YVO4/Nd:YVO4 crystal. The numerical solutions were in accordance with the experimental results.Ⅲ By simultaneously employing electro-optic (EO) modulator and Bi-doped GaAs, dual-loss-modulated Q-switched and mode-locking composite Nd:YVO4/Nd:YVO4/Nd:YVO4/KTP sub-nanosecond green laser was firstly demonstrated, the shortest sub-nanosecond pulse duration was 399 ps and the highest peak power was 1.1 MW, Compared with that of EO/GaAs, the Bi-doped GaAs could obtain better pulse laser, which was a promising saturable absorber with a value of application.Ⅳ With SESAM as saturable absorber, the passive mode-locking laser of multi-segment composite Nd:YVO4 crystal was investigated for the first time, then the relationship between pulse duration and intracavity power density was obtained theoretically, the theoretical analysises were in agreement with the experimental results.
Keywords/Search Tags:Solid-state laser, multi-segment composite Nd:YVO4 crystal, thermal lens effect, Q-switched, Q-switched and mode-locked, rate equqtions, Bi-GaAs, ultrafast laser, OPO
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